1. Field of the Invention
The present invention relates to a cosmetic and/or dermatological composition for topical use comprising an emulsion of the oil-in-water type formed from lipid vesicles dispersed in an aqueous phase containing at least one hydrophilic acidic active agent.
2. Description of the Background
It is known practice to introduce various active agents, which are intended to impart specific treatments to the skin and/or the hair, into cosmetic compositions. However, some of these active agents have the drawback of being unstable in aqueous media and of degrading readily on contact with the skin. Thus, they rapidly lose their activity over time and this instability runs counter to the desired efficacy.
A desired objective for a long time has been to formulate the likes of ascorbic acid or vitamin C, on account of its many beneficial properties, stably into a topical formulation. Ascorbic acid stimulates the synthesis of connective tissue and, in particular, of collagen. It reinforces the skin tissues"" defense against external attacking factors such as ultraviolet radiation and atmospheric pollutants; it compensates for vitamin E deficiency in the skin; it depigments the skin; and it has a free-radical-scavenging function. These last two properties make it an excellent candidate as a cosmetic or dermatological active agent for combating ageing of the skin or for preventing such ageing. Unfortunately, because of its chemical structure (an xcex1-keto lactose), ascorbic acid is highly sensitive to certain environmental parameters such as light, oxygen and water. Thus, ascorbic acid in ascorbic acid containing formulations frequently degrades when the formulations are exposed to these environmental parameters.
Several solutions have thus been suggested in the prior art for reducing and/or delaying the degradation of ascorbic acid in various preparations.
EP 0 679 387 discloses a composition comprising a hydrophilic support and ascorbic acid in pulverulent form. These ingredients are intended to be mixed together at the time of use. The support is described as comprising an aqueous medium and at least one hydrophilic gelling agent and as being capable of tolerating the introduction of an acidic compound. To do this, the gelling agent can be selected from polysaccharides, synthetic polymers and celluloses. A buffer is added to the solution so that the final pH of the composition is greater than 3.8.
Moreover, EP 0 642 781 discloses an emulsion of the oil-in-water type having a pH of less than 3.5, comprising, as stabilizer, a crosslinked anionic copolymer prepared by copolymerizing (i) acrylamide, (ii) 2-acrylamidomethylpropanesulfonic acid (AMPS), and (iii) at least one compound containing olefinic polyunsaturation as monomer components. The publication indicates that, at higher concentrations, the copolymer also exerts an emulsion-thickening function, such that the emulsion is presented as being able to have various fluidities ranging from that of milk to that of cream.
Finally, EP 0 755 673 discloses a topical composition comprising at least one water-sensitive active agent, such as ascorbic acid, stabilized with a combination of at least one polyol and at least one structuring agent selected from (meth)acrylic polymers and oils. The polyol, which is selected, for example, from propylene glycol, polyethylene glycol and glycerol, is present in an amount which is sufficient to impart a water activity value for the composition of less than or equal to 0.85.
These compositions of the prior art, which are formulated to stabilize ascorbic acid, have the drawback of being insufficiently viscous, or even insufficiently stable, at acidic pH, in particular, at a pH of from 2 to 4. It is thought that by maintaining the composition within this pH range, it is ensured that a large portion of the ascorbic acid will remain in protonated, uncharged form, in which form the penetration of the molecule into the skin is supposed to be facilitated. Furthermore, the large amount of polyol in the composition described in EP 755 673 imparts a relatively greasy feel to the composition, which certain users may find objectionable.
The low viscosity and/or stability of the known compositions containing ascorbic acid and which comprise a cosmetic gelling agent is very much such that, when the pH values of the compositions decrease down to a value ranging from 2 to 4, the ionic gelling agents the compositions contain undergo changes in their three-dimensional network. A variation in the van der Waals forces is also observed, implying nonionic gelling agents. The result of these changes is a reduction in the gelling power of these compounds, such that the emulsion containing these gelling agents transitions from having a creamy texture to the texture of a fluid such as a milk, or even such that the aqueous and oily phases of the emulsion separate, in extreme cases. The separation of the emulsion can be more or less gradual and/or more or less complete, depending on the case.
Other compositions of the prior art containing a hydrophilic, acidic active agent and a cosmetic gelling agent, and which thus pose the same problems of low viscosity and/or stability at acidic pH, are those described in FR-A-2 680 685 and EP 705 593. These are oil-in-water emulsions in which the oily phase is formed from lipid spheroids and in which the aqueous phase, gelled with a compound of the carbomer or xanthan gum type, contains, for example, a UV screening agent containing a sulfonic acid function. These compositions furthermore have the drawback that the lipid spheroids they contain are solid particles which are perceptible to the touch and have a particle size of 100 to 5000 xcexcm. The spheroids thus have a tendency, on account of their size, to become crushed on the surface of the skin, leading to mediocre penetration of the active agents they contain. A need, therefore, continues to exist for a composition, particularly for topical application, which provides enhanced stability for active agents susceptible to degradation over time.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a composition containing an acidic active agent and which has a viscosity greater than 500 centipoise at acidic pH, preferably at a pH of 2 to 4.
Another object of the present invention is to provide a composition containing an acidic active agent and which has good cosmetic properties, in particular, a non-greasy feel.
Still another object of the invention is to provide a composition having a water activity value of greater than 0.90, preferably greater than 0.95.
Briefly, these objects and other objects of the present invention as hereinafter will become more readily apparent can be attained by a composition for topical use, comprising an oil-in-water emulsion formed from lipid vesicles consisting of oily globules, each having a lamellar liquid crystal coating obtained from at least one surfactant, dispersed in an aqueous phase containing at least one hydrophilic acidic active agent but which does not contain a gelling agent.